Referring now to FIG. 1, in the known chloride process 10 for making titanium dioxide, a source of crude titanium dioxide (e.g., rutile ore) from hopper 11 is first reacted with chlorine from chlorine tank 12 and carbon (e.g., coke) from carbon hopper 13 in a chlorinator 14 to produce a gaseous stream 15 containing primarily titanium tetrachloride, carbon monoxide and carbon dioxide but also dust particles and other impurities. The titanium tetrachloride is condensed from stream 15 by condenser 16, purified by distillation, vaporized and then directed to burner 17 where the titanium tetrachloride is reacted with oxygen from oxygen tank 18 to produce a gaseous stream 19 containing primarily particulate titanium dioxide and chlorine gas.
A “support fuel”, (not shown) such as propane gas, can also be introduced into the burner 17 to increase the temperature in the burner 17. The stream 19 is then cooled in cooler 20 and then the particulate titanium dioxide is separated from the chlorine gas by gas/solids separator 21. The particulate titanium dioxide is then directed from gas/solids separator 21 to surface treatment tank 22 for further processing. The gaseous chlorine stream 25 from the gas/solids separator 21 is directed to a chlorine compressor 26 for recycle to the chlorinator 14. The gaseous chlorine stream 25 is called “burner tail gas”. The carbon monoxide, carbon dioxide, dust and other impurities from the condenser 16, called “chlorinator tail gas” 23 is treated by treatment system 24 to remove undesirable components (such as residual chlorine and carbon monoxide) and then vented.
The particulate titanium dioxide produced by the chloride process is used, for example, as a pigment in paints. A more detailed discussion of the chloride process for producing titanium dioxide can be found in Volume 24 of the Kirk-Othmer Encyclopedia of Chemical Technology (4th Ed., 1997) and in Volume I of the Pigment Handbook, Edited by Lewis (2nd Ed., 1988).
Referring still to FIG. 1, chemical analysis of the chlorinator tail gas 23 for residual chlorine allows for more effective control of the chlorinator 14. For example, if an excessive amount of chlorine is fed to the chlorinator 14, then the chlorinator tail gas 23 will contain relatively high levels of chlorine to be treated by treatment system 24. Therefore, samples of the chlorinator tail gas are periodically taken to a laboratory and analyzed for chlorine to better control the chlorinator 14. Similarly, chemical analysis of the burner tail gas 25 for oxygen allows for more effective control of the burner 17. For example, if an excessive amount of oxygen is fed to the burner 17, the excessive oxygen is wasted. Therefore, samples of the burner tail gas 25 are periodically taken to a laboratory and analyzed for oxygen. The burner tail gas 25 can also be analyzed for hydrogen chloride since the hydrogen chloride concentration of the burner tail gas 25 is a function of the amount of support fuel used in the burner 17. Frequent sampling and analysis of the chlorinator tail gas 23 and the burner tail gas 25 are desired for close control of the chlorinator 14 and the burner 17. However, manual sampling and analysis of the chlorinator tail gas 23 and the burner tail gas 25 is labor intensive, relatively expensive and limits process control.